Chirality in a helical structure originates from a unique conformation of a polymeric material. DNA and protein, which are the most common helical polymeric material, form a double helix, or a special helix, so-called α-helix, respectively. Both of them consist of only a single enantiomeric isomer having one rotational direction and have a stable right-handed structure. On the other hand, in order to have a left-handed structure, an enantiomeric isomer having opposite rotational direction, that is hardly found in the nature, should be employed as a structural unit.
Recently, artificially synthesized helical polymers have become well known. However, a stable helical polymer predominantly having one handedness often cannot be easily prepared by an asymmetric synthesis. Conventionally, a polymer having a single-handed helical structure should be prepared by using an optically active compound with corresponding handedness as an asymmetric center in the polymer structure (see, Patent Document 1). Thus, in order to obtain a helical structure with opposite handedness, other optically active compound having opposite handedness should be used as a reaction material.
Meanwhile, for a group of polymer which is called dynamic helical polymer, reversion between right-handedness and left-handedness occurs very fast in a solvent. Thus, by introducing a very small number of optically active sites to a side chain of the polymer, the handedness of the entire polymer molecule can be changed to a single one (see, Non-Patent Document 1). In this case, although around room temperature it is possible to observe a polymer having either right-handedness or left-handedness (see, Patent Document 2), since handedness of such polymer group can be easily reversed by temperature, a solvent and an optically active additive, etc. and the helix is dynamic by itself, the handedness of the polymer can be re-reversed depending on outer environments. Thus, practical use of such polymer as a functional material is very limited.
As explained above, producing a polymer having a stable single-handed helical structure, i.e., either right-handed or left-handed, from a single type of monomer remained as an impossible task to achieve until now.
A helical polymer with a static and stable single-handedness can be used as a filler for optical resolution column chromatography, a catalyst for asymmetric synthesis, and an optically active ligand material, etc. Thus, preparing right-handedness and left-handedness simply at low cost is very important to improve resolution efficiency and to obtain a desired optically active compound in asymmetric synthesis.
In addition, since in most cases a helical polymer has a very rigid main chain structure, it shows a cholesteric liquid crystal phase in a solvent or in a molten state (see, Patent Document 3). Inventors of the present invention also have developed a polymer with a very rigid main chain structure or use thereof as a liquid crystal (see, Patent Document 4 and 5).
As such, should the ratio between right-handedness and left-handedness be easily controlled in a main chain helix of a polymer, it becomes also possible to control a helical pitch (period of a helical structure) of a cholesteric liquid crystal phase. By immobilizing such structure as a film, an application to various optical devices can be also achieved simply at low cost.
As other examples of polymer having a rigid rod-like structure described above, lots of polyglutamic acid having a long n-alkyl chain, for instance n-decyl group, have been reported (see, Non-Patent Document 2, 3, 4 and 5). In this regard, it has been also reported that from polyglutamic acid having an alkyl chain longer than n-decyl group not only a characteristic of cholesteric liquid crystal but also hexagonal columnar and smectic phases are observed.
In addition, similar to the polyglutamic acid, some other rigid or semi-rigid polymers such as cellulose, polyisocyanate, polysilane and wholly aromatic polymers have been reported to have thermotropic liquid crystallinity or lyotropic liquid crystallinity.    Patent Document 1: JP-A 56-106907    Patent Document 2: JP-A 2001-294625    Patent Document 3: JP-A 2001-164251    Patent Document 4: WO 01/79310    Patent Document 5: WO 2005/080500    Non-Patent Document 1: E. Yashima, Modern Chemistry, 52 (2000)    Non-Patent Document 2: J. Watanabe, Y. Fukuda, R. Gehani and I. Uematsu, Macromolecules, 17, 1004 (1984)    Non-Patent Document 3: J. Watanabe, H. Ono, A. Abe and I. Uematsu, Macromolecules, 18, 2141 (1986)    Non-Patent Document 4: J. Watanabe, T. Nagase, H. Itoh, T. Ishii and T. Satoh, Mol. Cryst. Liq. Cryst., 164, 135 (1988)    Non-Patent Document 5: In “Ordering in Macromolecular Systems” A. Teramoto, M. Kobayashi and T. Norisue, Eds., Springer-Verlag, Berlin, Heidelberg, p 99-108 (1994)